METHOD FOR CASTING COMPOSITE INGOT

Description

Background of the Invention

1. Technical Field

[0001] This invention relates to a method and apparatus for casting composite metal ingots, as well as novel composite metal ingots thus obtained.

2. Background Art

[0002] For many years metal ingots, particularly aluminum or aluminum alloy ingots, have been produced by a semi-continuous casting process known as direct chill casting. In this procedure molten metal has been poured into the top of an open ended mould and a coolant, typically water, has been applied directly to the solidifying surface of the metal as it emerges from the mould.

[0003] Such a system is commonly used to produce large rectangular-section ingots for the production of rolled products, e.g. aluminum alloy sheet products. There is a large market for composite ingots consisting of two or more layers of different alloys. Such ingots are used to produce, after rolling, clad sheet for various applications such as brazing sheet, aircraft plate and other applications where it is desired that the properties of the surface be different from that of the core.

[0004] The conventional approach to such clad sheet has been to hot roll slabs of different alloys together to "pin" the two together, then to continue rolling to produce the finished product. This has a disadvantage in that the interface between the slabs is generally not metallurgically clean and bonding of the layers can be a problem.

[0005] There has also been an interest in casting layered ingots to produce a composite ingot ready for rolling. This has typically been carried out using direct chill (DC) casting, either by simultaneous solidification of two alloy streams or sequential solidification where one metal is solidified before being contacted by a second molten metal. A number of such methods are described in the literature that have met with varying degrees of success.

[0006] In Binczewski, U.S. Patent 4,567,936, issued February 4, 1986, a method is described for producing a composite ingot by DC casting where an outer layer of higher solidus temperature is cast about an inner layer with a lower solidus temperature. The disclosure states that the outer layer must be "fully solid and sound" by the time the lower solidus temperature alloy comes in contact with it.

[0007] Keller, German Patent 844 806, published July 24, 1952 describes a single mould for casting a layered structure where an inner core is cast in advance of the outer layer. In this procedure, the outer layer is fully solidified before the inner alloy contacts it.

[0008] In Robinson, U.S. Patent 3,353,934, issued November 21, 1967 a casting system is described where an internal partition is placed within the mould cavity to substantially separate areas of different alloy compositions. The end of the baffle is designed so that it terminates in the "mushy zone" just above the solidified portion of the ingot. Within the "mushy zone" alloy is free to mix under the end of the baffle to form a bond between the layers. However, the method is not controllable in the sense that the baffle used is "passive" and the casting depends on control of the sump location - which is indirectly controlled by the cooling system.

[0009] In Matzner, German patent DE 44 20 697, published December 21, 1995 a casting system is described using a similar internal partition to Robinson, in which the baffle sump position is controlled to allow for liquid phase mixing of the interface zone to create a continuous concentration gradient across the interface.

[0010] In Robertson et al, British patent GB 1,174,764, filed 21 December 1965 published 17 Dec 1969, a moveable baffle is provided to divide up a common casting sump and allow casting of two dissimilar metals. The baffle is moveable to allow in one limit the metals to completely intermix and in the other limit to cast two separate strands.

[0011] In Kilmer et al., WO Publication 2003/035305, published May 1, 2003 a casting system is described using a barrier material in the form of a thin sheet between two different alloy layers. The thin sheet has a sufficiently high melting point that it remains intact during casting, and is incorporated into the final product.

[0012] Takeuchi et al., U.S. Patent 4,828,015, issued May 9, 1989 describes a method of casting two liquid alloys in a single mould by creating a partition in the liquid zone by means of a magnetic field and feeding the two zones with separate alloys. The alloy that is to the upper part of the zone thereby forms a shell around the metal fed to the lower portion.

[0013] Veillette, U.S. Patent 3,911,996, describes a mould having an outer flexible wall for adjusting the shape of the ingot during casting.

[0014] Steen et al., U.S. Patent 5,947,184, describes a mould similar to Veillette but permitting more shape control.

[0015] Takeda et al., U.S. Patent 4,498,521 describes a metal level control system using a float on the surface of the metal to measure metal level and feedback to the metal flow control.

[0016] Odegard et al., U.S. Patent 5,526,870, describes a metal level control system using a remote sensing (radar) probe.

[0017] Wagstaff, U.S. Patent 6,260,602, describes a mould having a variably tapered wall to control the external shape of an ingot.

[0018] Binczewski, European Patent application no. EP 0 219 581 A1, describes a method and system for continuously casting a composite metal article in a direct chill mould. The molten metal is fed to different sides of a divider in the mold, and initial contact of the metals is between molten metal in a core and fully solidified metal in a cladding component.

[0019] It is an object of the present invention to produce a composite metal ingot consisting of two or more layers having an improved metallurgical bond between adjoining layers.

[0020] It is further object of the present invention to provide a means for controlling the interface temperature where two or more layers join in a composite ingot to improve the metallurgical bond between adjoining layers.

[0021] It is further object of the present invention to provide a means for controlling the interface shape where two or more alloys are combined in a composite metal ingot.

[0022] It is a further object of the present invention to provide a sensitive method for controlling the metal level in an ingot mould that is particularly useful in confined spaces.

Disclosure of the Invention

[0023] One embodiment of the present invention is a method for the casting of a composite metal ingot comprising at least two layers formed of one or more alloys compositions. The method comprises providing an open ended annular mould having a feed end and an exit end wherein molten metal is added at the feed end and a solidified ingot is extracted from the exit end. Divider walls are used to divide the feed end into at least two separate feed chambers, the divider walls terminating above the exit end of the mould, and where each feed chamber is adjacent at least one other feed chamber. For each pair of adjacent feed chambers a first stream of a first alloy is fed to one of the pair of feed chambers to form a pool of metal in the first chamber and a second stream of a second alloy is fed through the second of the pair of feed chambers to form a pool of metal in the second chamber. The first metal pool contacts the divider wall between the pair of chambers to cool the first pool so as to form a self-supporting surface adjacent the divider wall. The second metal pool is then brought into contact with the first pool so that the second pool first contacts the self-supporting surface of the first pool at a point where the temperature of the self-supporting surface is between the solidus and liquidus temperatures of the first alloy. The two alloy pools are thereby joined as two layers and cooled to form a composite ingot.

[0024] Preferably the second alloy initially contacts the self-supporting surface of the first alloy when the temperature of the second alloy is above the liquidus temperature of the second alloy. The first and second alloys may have the same alloy composition or may have different alloy compositions.

[0025] Preferably the upper surface of the second alloy contacts the self-supporting surface of the first pool at a point where the temperature of the self-supporting surface is between the solidus and liquidus temperatures of the first alloy.

[0026] In this embodiment of the invention the self-supporting surface may be generated by cooling the first alloy pool such that the surface temperature at the point where the second alloy first contacts the self-supporting surface is between the liquidus and solidus temperature.

[0027] Another embodiment of the present invention comprises a method for the casting of a composite metal ingot comprising at least two layers formed of one or more alloys compositions. This method comprises providing an open ended annular mould having a feed end and an exit end wherein molten metal is added at the feed end and a solidified ingot is extracted from the exit end. Divider walls are used to divide the feed end into at least two separate feed chambers, the divider walls terminating above the exit end of the mould, and where each feed chamber is adjacent at least one other feed chamber. For each pair of adjacent feed chambers a first stream of a first alloy is fed to one of the pair of feed chambers to form a pool of metal in the first chamber and a second stream of a second alloy is fed through the second of the pair of feed chambers to form a pool of metal in the second chamber. The first metal pool contacts the divider wall between the pair of chambers to cool the first pool so as to form a self-supporting surface adjacent the divider wall. The second metal pool is then brought into contact with the first pool so that the second pool first contacts the self-supporting surface of the first pool at a point where the temperature of the self-supporting surface is below the solidus temperature of the first alloy to form an interface between the two alloys. The interface is then reheated to a temperature between the solidus and liquidus temperature of the first alloy so that the two alloy pools are thereby joined as two layers and cooled to form a composite ingot.

[0028] In this embodiment the reheating is preferably achieved by allowing the latent heat within the first or second alloy pools to reheat the surface.

[0029] Preferably the second alloy initially contacts the self-supporting surface of the first alloy when the temperature of the second alloy is above the liquidus temperature of the second alloy. The first and second alloys may have the same alloy composition or may have different alloy compositions.

[0030] Preferably the upper surface of the second alloy contacts the self-supporting surface of the first pool at a point where the temperature of the, self-supporting surface is between the solidus and liquidus temperatures of the first alloy.

[0031] The self-supporting surface may also have an oxide layer formed on it. It is sufficiently strong to support the splaying forces normally causing the metal to spread out when unconfined. These splaying forces include the forces created by the metallostatic head of the first stream, and expansion of the surface in the case where cooling extends below the solidus followed by re-heating the surface. By bringing the liquid second alloy into first contact with the first alloy while the first alloy is still in the semi-solid state or, and in the alternate embodiment, by ensuring that the interface between the alloys is reheated to a semi-solid state, a distinct but joining interface layer is formed between the two alloys. Furthermore, the fact that the interface between the second alloy layer and the first alloy is thereby formed before the first alloy layer has developed a rigid shell means that stresses created by the direct application of coolant to the exterior surface of the ingot are better controlled in the finished product, which is particularly advantageous when casting crack prone alloys.

[0032] The result of the present invention is that the interface between the first and second alloy is maintained, over a short length of emerging ingot, at a temperature between the solidus and liquidus temperature of the first alloy. In one particular embodiment, the second alloy is fed into the mould so that the upper surface of the second alloy in the mould is in contact with the surface of the first alloy where the surface temperature is between the solidus and liquidus temperature and thus an interface having met this requirement is formed. In an alternate embodiment, the interface is reheated to a temperature between the solidus and liquidus temperature shortly after the upper surface of the second alloy contacts the self-supporting surface of the first alloy. Preferably the second alloy is above its liquidus temperature when it first contacts the surface of the first alloy. When this is done, the interface integrity is maintained but at the same time, certain alloy components are sufficiently mobile across the interface that metallurgical bonding is facilitated.

[0033] If the second alloy is contacted where the temperature of the surface of the first alloy is sufficiently below the solidus (for example after a significant solid shell has formed), and there is insufficient latent heat to reheat the interface to a temperature between the solidus and liquidus temperatures of the first alloy, then the mobility of alloy components is very limited and a poor metallurgical bond is formed. This can cause layer separation during subsequent processing.

[0034] If the self-supporting surface is not formed on the first alloy prior to the second alloy contacting the first alloy, then the alloys are free to mix and a diffuse layer or alloy concentration gradient is formed at the interface, making the interface less distinct.

[0035] It is particularly preferred that the upper surface of the second alloy be maintained a position below the bottom edge of the divider wall. If the upper surface of the second alloy in the mould lies above the point of contact with the surface of the first alloy, for example, above the bottom edge of the divider wall, then there is a danger that the second alloy can disrupt the self supporting surface of the first alloy or even completely re-melt the surface because of excess latent heat. If this happens, there may be excessive mixing of alloys at the interface, or in some cases runout and failure of the cast. If the second alloy contacts the divider wall particularly far above the bottom edge, it may even be prematurely cooled to a point where the contact with the self-supporting surface of the first alloy no longer forms a strong metallurgical bond. In certain cases it may however be advantageous to maintain the upper surface of the second alloy close to the bottom edge of the divider wall but slightly above the bottom edge so that the divider wall can act as an oxide skimmer to prevent oxides from the surface of the second layer from being incorporated in the interface between the two layers. This is particularly advantageous where the second alloy is prone to oxidation. In any case the upper surface position must be carefully controlled to avoid the problems noted above, and should not lie more than about 3 mm above the bottom end of the divider.

[0036] In all of the preceding embodiments it is particularly advantageous to contact the second alloy to the first at a temperature between the solidus and coherency temperature of the first alloy or to reheat the interface between the two to a temperature between the solidus and coherency temperature of the first alloy. The coherency point, and the temperature (between the solidus and liquidus temperature) at which it occurs is an intermediate stage in the solidification of the molten metal. As dendrites grow in size in a cooling molten metal and start to impinge upon one another, a continuous solid network builds up throughout the alloy volume. The point at which there is a sudden increase in the torque force needed to shear the solid network is known as the "coherency point". The description of coherency point and its determination can be found in Solidification Characteristics of Aluminum Alloys Volume 3 Dendrite Coherency Pg 210.

[0037] In another embodiment of the invention, there is provided an apparatus for casting metal comprising an open ended annular mould having a feed end and an exit end and a bottom block that can fit within the exit end and is movable in a direction along the axis of the annular mould. The feed end of the mould is divided into at least two separate feed chambers, where each feed chamber is adjacent at least one other feed chamber and where the adjacent feed chambers are separated by a temperature controlled divider wall that can add or remove heat. The divider wall ends above the exit end of the mould. Each chamber includes a metal level control apparatus such that in adjacent pairs of chambers the metal level in one chamber can be maintained at a position above the lower end of the divider wall between the chambers and in the other chamber can be maintained at a different position from the level in the first chamber.

[0038] Preferably the level in the other chamber is maintained at a position below the lower end of the divider wall.

[0039] The divider wall is designed so that the heat extracted or added is calibrated so as to create a self-supporting surface on metal in the first chamber adjacent the divider wall and to control the temperature of the self-supporting surface of the metal in the first chamber to lie between the solidus and liquidus temperature at a point where the upper surface of the metal in the second chamber can be maintained.

[0040] The temperature of the self-supporting layer can be carefully controlled by removing heat from the divider wall by a temperature control fluid being passed through a portion of the divider wall or being brought into contact with the divider wall at its upper end to control the temperature of the self-supporting layer.

[0041] A further embodiment of the invention is a method for the casting of a composite metal ingot comprising at least two different alloys, which comprises providing an open ended annular mould having a feed end and an exit end and means for dividing the feed end into at least two separate, feed chambers, where each feed chamber is adjacent at least one other feed chamber. For each pair of adjacent feed chambers, a first stream of a first alloy is fed through one of the adjacent feed chambers into said mould, a second stream of a second alloy is fed through another of the adjacent feed chambers. A temperature controlling divider wall is provided between the adjacent feed chambers such that the point on the interface where the first and second alloy initially contact each other is maintained at a temperature between the solidus and liquidus temperatures of the first alloy by means of the temperature controlling divider wall whereby the alloy streams are joined as two layers. The joined alloy layers are cooled to form a composite ingot.

[0042] The second alloy is preferably brought into contact with the first alloy immediately below the bottom of the divider wall without first contacting the divider wall. In any event, the second alloy should contact the first alloy no less than about 2 mm below the bottom edge of the divider wall but not greater than 20 mm and preferably about 4 to 6 mm below the bottom edge of the divider wall.

[0043] If the second alloy contacts the divider wall before contacting the first alloy, it may be prematurely cooled to a point where the contact with the self-supporting surface of the first alloy no longer forms a strong metallurgical bond. Even if the liquidus temperature of the second alloy is sufficiently low that this does not happen, the metallostatic head that would exist may cause the second alloy to feed up into the space between the first alloy and the divider wall and cause casting defects or failure. When the upper surface of the second alloy is desired to be above the bottom edge of the divider wall (e.g. to skim oxides) it must be carefully controlled and positioned as close as practically possible to the bottom edge of the divider wall to avoid these problems.

[0044] The divider wall between adjacent pairs of feed chambers may be tapered and the taper may vary along the length of the divider wall. The divider wall may further have a curvilinear shape. These features can be used to compensate for the different thermal and solidification properties of the alloys used in the chambers separated by the divider wall and thereby provide for control of the final interface geometry within the emerging ingot. The curvilinear shaped wall may also serve to form ingots with layers having specific geometries that can be rolled with less waste. The divider wall between adjacent pairs of feed chambers may be made flexible and may be adjusted to ensure that the interface between the two alloy layers in the final cast and rolled product is straight regardless of the alloys used and is straight even in the start-up section.

[0045] A further embodiment of the invention is an apparatus for casting of composite metal ingots, comprising an open ended annular mould having a feed end and an exit end and a bottom block that can fit inside the exit end and move along the axis of the mould. The feed end of the mould is divided into at least two separate feed chambers, where each feed chamber is adjacent at least one other feed chamber and where the adjacent feed chambers are separated by a divider wall. The divider wall is flexible, and a positioning device is attached to the divider wall so that the wall curvature in the plane of the mould can be varied by a predetermined amount during operation.

[0046] A further embodiment of the invention is a method for the casting of a composite metal ingot comprising at least two different alloys, which comprises providing an open ended annular mould having a feed end and an exit end and means for dividing the feed end into at least two separate, feed chambers, where each feed chamber is adjacent at least one other feed chamber. For adjacent pairs of the feed chambers, a first stream of a first alloy is fed through one of the adjacent feed chambers into the mould, and a second stream of a second alloy is fed through another of the adjacent feed chambers. A flexible divider wall is provided between adjacent feed chambers and the curvature of the flexible divider wall is adjusted during casting to control the shape of interface where the alloys are joined as two layers. The joined alloy layers are then cooled to form a composite ingot.

[0047] The metal feed requires careful level control and one such method is to provide a slow flow of gas, preferably inert, through a tube with an opening at a fixed point with respect to the body of the annular mould. The opening is immersed in use below the surface of the metal in the mould, the pressure of the gas is measured and the metallostatic head above the tube opening is thereby determined. The measured pressure can therefore be used-to directly control the metal flow into the mould so as to maintain the upper surface of the metal at a constant level.

[0048] A further embodiment of the invention is a method of casting a metal ingot which comprises providing an open ended annular mould having a feed end and an exit end, and feeding a stream of molten metal into the feed end of said mould to create a metal pool within said mould having a surface. The end of a gas delivery tube is immersed into the metal pool from the feed end of mould tube at a predetermined position with respect to the mould body and an inert gas is bubbled though the gas delivery tube at a slow rate sufficient to keep the tube unfrozen. The pressure of the gas within the said tube is measured to determine the position of the molten metal surface with respect to the mould body.

[0049] A further embodiment of the invention is an apparatus for casting a metal ingot that comprises an open-ended annular mould having a feed end and an exit end and a bottom block that fits in the exit end and is movable along the axis of the mould. A metal flow control device is provided for controlling the rate at which metal can flow into the mould from an external source, and a metal level sensor is also provided comprising a gas delivery tube attached to a source of gas by means of a gas flow controller and having an open end positioned at a predefined location below the feed end of the mould, such that in use, the open end of the tube would normally lie below the metal level in the mould. A means is also provided for measuring the pressure of the gas in the gas delivery tube between the flow controller and the open end of the gas delivery tube, the measured pressure of the gas being adapted to control the metal flow control device so as to maintain the metal into which the open end of the gas delivery tube is placed at a predetermined level.

[0050] This method and apparatus for measuring metal level is particularly useful in measuring and controlling metal level in a confined space such as in some or all of the feed chambers in a multi-chamber mould design. It may be used in conjunction with other metal level control systems that use floats or similar surface position monitors, where for example, a gas tube is used in smaller feed chambers and a feed control system based on a float or similar device in the larger feed chambers.

[0051] In one preferred embodiment of the present invention there is provided a method for casting a composite ingot having two layer of different alloys, where one alloy forms a layer on the wider or "rolling" face of a rectangular cross-sectional ingot formed from another alloy. For this procedure there is provided an open ended annular mould having a feed end and an exit end and means for dividing the feed end into separate adjacent feed chambers separated by a temperature controlled divider wall. The first stream of a first alloy is fed though one of the feed chambers into the mould and a second stream of a second alloy is fed through another of the feed chambers, this second alloy having a lower liquidus temperature than the first alloy. The first alloy is cooled by the temperature controlled divider wall to form a self-supporting surface that extends below the lower end of the divider wall and the second alloy is contacted with the self-supporting surface of the first alloy at a location where the temperature of the self-supporting surface is maintained between the solidus and liquidus temperature of the first alloy, whereby the two alloy streams are joined as two layers. The joined alloy layers are then cooled to form a composite ingot.

[0052] In another preferred embodiment the two chambers are configured so that an outer chamber completely surrounds the inner chamber whereby an ingot is formed having a layer of one alloy completely surrounding a core of a second alloy.

[0053] A preferred embodiment includes two laterally spaced temperature controlled divider walls forming three feed chambers. Thus, there is a central feed chamber with a divider wall on each side and a pair of outer feed chambers on each side of the central feed chamber. A stream of the first alloy may be fed through the central feed chamber, with streams of the second alloy being fed into the two side chambers. Such an arrangement is typically used for providing two cladding layers on a central core material.

[0054] It is also possible to reverse the procedure such that streams of the first alloy are feed through the side chambers while a stream of the second alloy is fed through the central chamber. With this arrangement, casting is started in the side feed chambers with the second alloy being fed through the central chamber and contacting the pair of first alloys immediately below the divider walls.

[0055] The ingot cross-sectional shape may be any convenient shape (for example circular, square, rectangular or any other regular or irregular shape) and the cross-sectional shapes of individual layers may also vary within the ingot.

[0056] Another embodiment of the invention is a cast ingot product consisting of an elongated ingot comprising, in cross-section, two or more separate alloy layers of differing composition, wherein the interface between adjacent alloys layers is in the form of a substantially continuous metallurgical bond. This bond is characterized by the presence of dispersed particles of one or more intermetallic compositions of the first alloy in a region of the second alloy adjacent the interface. Generally in the present invention the first alloy is the one on which a self-supporting surface is first formed and the second alloy is brought into contact with this surface while the surface temperature is between the soldidus and liquidus temperature of the first alloy, or the interface is subsequently reheated to a temperature between the solidus and liquidus temperature of the first alloy. The dispersed particles preferably are less than about 20 µm in diameter and are found in,a region of up to about 200 µm from the interface.

[0057] The bond may be further characterized by the presence of plumes or exudates of one or more intermetallic compositions of the first alloy extending from the interface into the second alloy in the region adjacent the interface. This feature is particularly formed when the temperature of the self-supporting surface has not been reduced below the solidus temperature prior to contact with the second alloy.

[0058] The plumes or exudates preferably penetrate less than about 100 µm into the second alloy from the interface.

[0059] Where the intermetallic compositions of the first alloy are dispersed or exuded into the second alloy, there remains in the first alloy, adjacent to the interface between the first and second alloys, a layer which contains a reduced quantity of the intermetallic particles and which consequently can form a layer which is more noble than the first alloy and may impart corrosion resistance to the clad material. This layer is typically 4 to 8 mm thick.

[0060] This bond may be further characterized by the presence of a diffuse layer of alloy components of the first alloy in the second alloy layer adjacent the interface. This feature is particularly formed in instances where the surface of the first alloy is cooled below the solidus temperature of the first alloy and then the interface between first and second alloy is reheated to between the solidus and liquidus temperatures.

[0061] Although not wishing to be bound by any theory, it is believed that the presence of these features is caused by formation of segregates of intermetallic compounds of the first alloy at the self supporting surface formed on it with their subsequent dispersal or exudation into the second alloy after it contacts the surface. The exudation of intermetallic compounds is assisted by splaying forces present at the interface.

[0062] A further feature of the interface between layers formed by the methods of this invention is the presence of alloy components from the second alloy between the grain boundaries of the first alloy immediately adjacent the interface between the two alloys. It is believed that these arise when the second alloy (still generally above its liquidus temperature) comes in contact with the self-supporting surface of the first alloy (at a temperature between the solidus and liquidus temperature of the first alloy). Under these specific conditions, alloy component of the second alloy can diffuse a short distance (typically about 50 µm) along the still liquid grain boundaries, but not into the grains already formed at the surface of the first alloy. If the interface temperature in above the liquidus temperature of both alloys, general mixing of the alloys will occur, and the second alloy components will be found within the grains as well as grain boundaries. If the interface temperature is below the solidus temperature of the first alloy, there will be not opportunity for grain boundary diffusion to occur.

[0063] The specific interfacial features described are specific features caused by solid state diffusion, or diffusion or movement of elements along restricted liquid paths and do not affect the generally distinct nature of the overall interface.

[0064] Regardless how the interface is formed, the unique structure of the interface provides for a strong metallurgical bond at the interface and therefore makes the structure suitable for rolling to sheet without problems associated with delamination or interface contamination.

[0065] In yet a further embodiment of the invention, there is a composite metal ingot, comprising at least two layers of metal, wherein pairs of adjacent layers are formed by contacting the second metal layer to the surface of the first metal layer such that the when the second metal layer first contacts the surface of the first metal layer the surface of the first metal layer is at a temperature between its liquidus and solidus temperature and the temperature of the second metal layer is above its liquidus temperature. Preferably the two metal layers are composed of different alloys.

[0066] Similarly in yet a further embodiment of the invention, there is a composite metal ingot, comprising at least two layers of metal, wherein pairs of adjacent layers are formed by contacting the second metal layer to the surface of the first metal layer such that the when the second metal layer first contacts the surface of the first metal layer the surface of the first metal layer is at a temperature below its solidus temperature and the temperature of the second metal layer is above its liquidus temperature, and the interface formed between the two metal layers is subsequently reheated to a temperature between the solidus and liquidus temperature of the first alloy. Preferably the two metal layers are composed of different alloys.

[0067] In one preferred embodiment, the ingot is rectangular in cross section and comprises a core of the first alloy and at least one surface layer of the second alloy, the surface layer being applied to the long side of the rectangular cross-section. This composite metal ingot is preferably hot and cold rolled to form a composite metal sheet.

[0068] In one particularly preferred embodiment, the alloy of the core is an aluminum-manganese alloy and the surface alloy is an aluminum-silicon alloy. Such composite ingot when hot and cold rolled to form a composite metal brazing sheet that may be subject to a brazing operation to make a corrosion resistant brazed structure.

[0069] In another particularly preferred embodiment, the alloy core is a scrap aluminum alloy and the surface alloy a pure aluminum alloy. Such composite ingots when hot and cold rolled to form composite metal sheet provide for inexpensive recycled products having improved properties of corrosion resistance, surface finishing capability, etc. In the present context a pure aluminum alloy is an aluminum alloy having a thermal conductivity greater than 190 watts/m/K and a solidification range of less than 50°C.

[0070] In yet another particularly preferred embodiment the alloy core is a high strength non-heat treatable alloy (such as an Al-Mg alloy) and the surface alloy is a brazeable alloy (such as an Al-Si alloy). Such composite ingots when hot and cold rolled to form composite metal sheet may be subject to a forming operation and used for automotive structures which can then be brazed or similarly joined.

[0071] In yet another particularly preferred embodiment the alloy core is a high strength heat treatable alloy (such as an 2xxx alloy) and the surface alloy is a pure aluminum alloy. Such composite ingots when hot and cold rolled form composite metal sheet suitable for aircraft structures. The pure alloy may be selected for corrosion resistance or surface finish and should preferably have a solidus temperature greater than the solidus temperature of the core alloy.

[0072] In yet another particularly preferred embodiment the alloy core is a medium strength heat treatable alloy (such as an Al-Mg-Si alloy) and the surface alloy is a pure aluminum alloy. Such composite ingots when hot and cold rolled form composite metal sheet suitable for automotive closures. The pure alloy may be selected for corrosion resistance or surface finish and should preferably have a solidus temperature greater than the solidus temperature of the core alloy.

[0073] In another preferred embodiment, the ingot is cylindrical in cross-section and comprises a core of the first alloy and a concentric surface layer of the second alloy. In yet another preferred embodiment, the ingot is rectangular or square in cross-section and comprises a core of the second alloy and a annular surface layer of the first alloy.

Brief Description of the Drawings

[0074] In the drawings which illustrate certain preferred embodiments of this invention:

Fig. 1 is an elevation view in partial section showing a single divider wall;

Fig. 2 is a schematic illustration of the contact between the alloys;

Fig. 3 is an elevation view in partial section similar to Fig. 1, but showing a pair of divider walls;

Fig. 4 is an elevation view in partial section similar to Fig. 3, but with the second alloy having a lower liquidus temperature than the first alloy being fed into the central chamber;

Figs. 5a, 5b and 5c are plan views showing some alternative arrangements of feed chamber that may be used with the present invention;

Fig. 6 is an enlarged view in partial section of a portion of Fig. 1 showing a curvature control system;

Fig. 7 is a plan view of a mould showing the effects of variable curvature of the divider wall;

Fig. 8 is an enlarged view of a portion of Fig. 1 illustrating a tapered divider wall between alloys;

Fig. 9 is a plan view of a mould showing a particularly preferred configuration of a divider wall;

Fig. 10 is a schematic view showing the metal level control system of the present invention;

Fig. 11 is a perspective view of a feed system for one of the feed chambers of the present invention;

Fig. 12 is a plan view of a mould showing another preferred configuration of the divider wall;

Fig. 13 is a microphotograph of a section through the joining face between a pair of adjacent alloys using the method of the present invention showing the formation of intermetallic particles in the opposite alloy;

Fig. 14 is a microphotograph of a section through the same joining face as in Fig. 13 showing the formation of intermetallic plumes or exudates;

Fig. 15 is a microphotograph of a section through the joining face between a pair of adjacent alloys processed under conditions outside the scope of the present invention;

Fig. 16 is a microphotograph of a section through the joining face between a cladding alloy layer and a cast core alloy using the method of the present invention;

Fig. 17 is a microphotograph of a section through the joining face between a cladding alloy layer and a cast core alloy using the method of the present invention, and illustrating the presence of components of core alloy solely along grain boundaries of the cladding alloy at the joining face;

Fig. 18 a microphotograph of a section through the joining face between a cladding alloy layer and a cast core alloy using the method of the present invention, and illustrating the presence of diffused alloy components as in Figure 17; and

Fig. 19 a microphotograph of a section through the joining face between a cladding alloy layer and a cast core alloy using the method of the present invention, and also illustrating the presence of diffused alloy components as in Figure 17.

Best Modes for Carrying Out the Invention

[0075] With reference to Fig. 1, rectangular casting mould assembly 10 has mould walls 11 forming part of a water jacket 12 from which a stream of cooling water 13 is dispensed.

[0076] The feed portion of the mould is divided by a divider wall 14 into two feed chambers. A molten metal delivery trough 30 and delivery nozzle 15 equipped with an adjustable throttle 32 feeds a first alloy into one feed chamber and a second metal delivery trough 24 equipped with a side channel, delivery nozzle 16 and adjustable throttle 31 feeds a second alloy into a second feed chamber. The adjustable throttles 31, 32 are adjusted either manually or responsive to some control signal to adjust the flow of metal into the respective feed chambers. A vertically movable bottom block unit 17 supports the embryonic composite ingot being formed and fits into the outlet end of the mould prior to starting a cast and thereafter is lowered to-allow the ingot to form.

[0077] As more clearly shown with reference to Figure 2, in the first feed chamber, the body of molten metal 18 gradually cools so as to form a self-supporting surface 27 adjacent the lower end of the divider wall and then forms a zone 19 that is between liquid and solid and is often referred as a mushy zone. Below this mushy or semi-solid zone is a solid metal alloy 20. Into the second feed chamber is fed a second alloy liquid flow 21 having a lower liquidus temperature than the first alloy 18. This metal also forms a mushy zone 22 and eventually a solid portion 23.

[0078] The self-supporting surface 27 typically undergoes a slight contraction as the metal detaches from the divider wall 14 then a slight expansion as the splaying forces caused, for example, by the metallostatic head of the metal 18 coming to bear. The self-supporting surface has sufficient strength to restrain such forces even though the temperature of the surface may be above the solidus temperature of the metal 18. An oxide layer on the surface can contribute to this balance of forces.

[0079] The temperature of the divider wall 14 is maintained at a predetermined target temperature by means of a temperature control fluid passing through a closed channel 33 having an inlet 36 and outlet 37 for delivery and removal of temperature control fluid that extracts heat from the divider wall so as to create a chilled interface which serves to control the temperature of the self supporting surface 27 below the lower end of the divider wall 35. The upper surface 34 of the metal 21 in the second chamber is then maintained at a position below the lower edge 35 of the divider wall 14 and at the same time the temperature of the self supporting surface 27 is maintained such that the surface 34 of the metal 21 contacts this self supporting surface 27 at a point where the temperature of the surface 27 lies between the solidus and liquidus temperature of the metal 18. Typically the surface 34 is controlled at a point slightly below the lower edge 35 of the divider wall 14, generally within about 2 to 20 mm from the lower edge. The interface layer thus formed between the two alloy streams at this point forms a very strong metallurgical bond between the two layers without excessive mixing of the alloys.

[0080] The coolant flow (and temperature) required to establish the temperature of the self-supporting surface 27 of metal 18 within the desired range is generally determined empirically by use of small thermocouples that are embedded in the surface 27 of the metal ingot as it forms and once established for a given composition and casting temperature for metal 18 (casting temperature being the temperature at which the metal 18 is delivered to the inlet end of the feed chamber) forms, part of the casting practice for such an alloy. It has been found in particular that at a fixed coolant flow through the channel 33, the temperature of the coolant exiting the divider wall coolant channel measured at the outlet 37 correlates well with the temperature of the self supporting surface of the metal at predetermined locations below the bottom edge of the divider wall, and hence provides for a simple and effective means of controlling this critical temperature by providing a temperature measuring device such as a thermocouple or thermistor 40 in the outlet of the coolant channel.

[0081] Fig. 3 is essentially the same mould as in Fig. 1, but in this case a pair of divider walls 14 and 14a are used dividing the mouth of the mould into three feed chambers. There is a central chamber for the first metal alloy and a pair of outer feed chambers for a second metal alloy. The outer feed chambers may be adapted for a second and third metal alloy, in which case the lower ends of the divider walls 14 and 14a may be positioned differently and the temperature control may differ for the two divider walls depending on the particular requirements for casting and creating strongly bonded interfaces between the first and second alloys and between the first and third alloys.

[0082] As shown in Fig. 4, it is also possible to reverse the alloys so that the first alloy streams are fed into the outer feed chambers and a second alloy stream is fed into the central feed chamber.

[0083] Figure 5 shows several more complex chamber arrangements in plan view. In each of these arrangements there is an outer wall 11 shown for the mould and the inner divider walls 14 separating the individual chambers. Each divider wall 14 between adjacent chambers must be positioned and thermally controlled such that the conditions for casting described herein are maintained. This means that the divider walls may extend downwards from the inlet of the mould and terminate at different positions and may be controlled at different temperatures and the metal levels in each chamber may be controlled at different levels in accordance with the requirements of the casting practice.

[0084] It is advantageous to make the divider wall 14 flexible or capable of having a variable curvature in the plane of the mould as shown in Figures 6 and 7. The curvature is normally changed between the start-up position 14' and steady state position 14 so as to maintain a constant interface throughout the cast. This is achieved by means of an arm 25 attached at one end to the top of the divider wall 14 and driven in a horizontal direction by a linear actuator 26. If necessary the actuator is protected by a heat shield 42.

[0085] The thermal properties of alloys vary considerably and the amount and degree of variation in the curvature is predetermined based on the alloys selected for the various layers in the ingot. Generally these are determined empirically as part of a casting practice for a particular product.

[0086] As shown in Figure 8 the divider wall 14 may also be tapered 43 in the vertical direction on the side of the metal 18. This taper may vary along the length of the divider wall 14 to further control the shape of the interface between adjacent alloy layer. The taper may also be used on the outer wall 11 of the mould. This taper or shape can be established using principals, for example, as described in U.S. 6,260,602 (Wagstaff) and will again depend on the alloys selected for the adjacent layers.

[0087] The divider wall 14 is manufactured from metal (steel or aluminum for example) and may in part be manufactured from graphite, for example by using a graphite insert 46 on the tapered surface. Oil delivery channels 48 and grooves 47 may also be used to provide lubricants or parting substances. Of course inserts and oil delivery configurations may be used on the outer walls in manner known in the art.

[0088] A particular preferred embodiment of divider wall is shown in Figure 9. The divider wall 14 extends substantially parallel to the mould sidewall 11 along one or both long (rolling) faces of a rectangular cross section ingot. Near the ends of the long sides of the mould, the divider wall 14 has 90° curves 45 and is terminated at locations 50 on the long side wall 11, rather than extending fully to the short side walls. The clad ingot cast with such a divider wall can be rolled to better maintain the shape of the cladding over the width of the sheet than occurs in more conventional roll-cladding processes. The taper described in Figure 8 may also be applied to this design, where for example, a high degree of taper may be used at curved surface 45 and a medium degree of taper on straight section 44.

[0089] Figure 10 shows a method of controlling the metal level in a casting mould which can be used in any casting mould, whether or not for casting layered ingots, but is particularly useful for controlling the metal level in confined spaces as may be encountered in some metal chambers in moulds for casting multiple layer ingots. A gas supply 51 (typically a cylinder of inert gas) is attached to a flow controller 52 that delivers a small flow of gas to a gas delivery tube with an open end.53 that is positioned at a reference location 54 within the mould. The inside diameter of the gas delivery tube at its exit is typically between 3 to 5 mm. The reference location is selected so as to be below the top surface of the metal 55 during a casting operation, and this reference location may vary depending on the requirements of the casting practice.

[0090] A pressure transducer 56 is attached to the gas delivery tube at a point between the flow controller and the open end so as to measure the backpressure of gas in the tube. This pressure transducer 56 in turn produces a signal that can be compared to a reference signal to control the flow of metal entering the chamber by means known to those skilled in the art. For example an adjustable refractory stopper 57 in a refractory tube 58 fed in turn from a metal delivery trough 59 may be used. In use, the gas flow is adjusted to a low level just sufficient to maintain the end of the gas delivery tube open. A piece of refractory fibre inserted in the open end of the gas delivery tube is used to dampen the pressure fluctuations caused by bubble formation. The measured pressure then determines the degree of immersion of the open end of the gas delivery tube below the surface of the metal in the chamber and hence the level of the metal surface with respect to the reference location and the flow rate of metal into the chamber is therefore controlled to maintain the metal surface at a predetermined position with respect to the reference location.

[0091] The flow controller and pressure transducer are devices that are commonly available devices. It is particularly preferred however that the flow controller be capable of reliable flow control in the range of 5 to 10 cc/minute of gas flow. A pressure transducer able to measure pressures to about 0.1 psi (0.689 kPa) provides a good measure of metal level control (to within 1 mm) in the present invention and the combination provides for good control even in view of slight fluctuations in the pressure causes by the slow bubbling through the open end of the gas delivery tube.

[0092] Figure 11 shows a perspective view of a portion of the top of the mould of the present invention. A feed system for one of the metal chambers is shown, particularly suitable for feeding metal into a narrow feed chamber as may be used to produce a clad surface on an ingot. In this feed system, a channel 60 is provided adjacent the feed chamber having several small down spouts 61 connected to it which end below the surface of the metal. Distribution bags 62 made from refractory fabric by means known in the art are installed around the outlet of each down spout 61 to improve the uniformity of metal distribution and temperature. The channel in turn is fed from a trough 68 in which a single down spout 69 extends into the metal in the channel and in which is inserted a flow control stopper (not shown) of conventional design. The channel is positioned and leveled so that metal flows uniformly to all locations.

[0093] Figure 12 shows a further preferred arrangement of divider walls 14 for casting a rectangular cross-section ingot clad on two faces. The divider walls have a straight section 44 substantially parallel to the mould sidewall 11 along one or both long (rolling) faces of a rectangular cross section ingot. However, in this case each divider wall has curved end portions 49 which intersect the shorter end wall of the mould at locations 41. This is again useful in maintaining the shape of the cladding over the width of the sheet than occurs in more conventional roll-cladding processes. Whilst illustrated for cladding on two faces, it can equally well be used for cladding on a single face of the ingot.

[0094] Figure 13 is a microphotograph at 15X magnification showing the interface 80 between an A1-Mn alloy 81 (X-904 containing 0.74% by weight Mn, 0.55% by weight Mg, 0.3% by weight Cu, 0.17 % by weight, 0.07% by weight Si and the balance Al and inevitable impurities) and an Al-Si alloy 82(AA4147 containing 12% by weight Si, 0.19% by weight Mg and the balance Al and inevitable impurities) cast under the conditions of the present invention. The Al-Mn alloy had a solidus temperature of 1190°F (643°C) and a liquidus temperature of 1215°F (657°C). The Al-Si alloy had a solidus temperature of 1070°F (576°C) and a liquidus temperature of 1080°F (582°C). The Al-Si alloy was fed into the casting mould such that the upper surface of the metal was maintained so that it contacted the Al-Mn alloy at a location where a self-supporting surface has been established on the Al-Mn alloy, but its temperature was between the solidus and liquidus temperatures of the Al-Mn alloy.

[0095] A clear interface is present on the sample indicating no general mixing of alloys, but in addition, particles of intermetallic compounds containing Mn 85 are visible in an approximately 200 µm band within the A1-Si alloy 82 adjacent the interface 80 between the Al-Mn and Al-Si alloys. The intermetallic compounds are mainly MnAl₆ and alpha-AlMn.

[0096] Figure 14 is a microphotograph at 200X magnification showing the interface 80 of the same alloy combination as in Figure 13 where the self-surface temperature was not allowed to fall below the solidus temperature of the Al-Mn alloy prior to the Al-Si alloy contacting it. A plume or exudate 88 is observed extending from the interface 80 into the Al-Si alloy 82 from the A1-Mn alloy 81 and the plume or exudate has a intermetallic composition containing Mn that is similar to the particles in Figure 13. The plumes or exudates typically extend up to 100 µm into the neighbouring metal. The resulting bond between the alloys is a strong metallurgical bond. Particles of intermetallic compounds containing Mn 85 are also visible in this microphotograph and have a size typically up to 20 µm.

[0097] Figure 15 is a microphotograph (at 300X magnification) showing the interface between an Al-Mn alloy (AA3003) and an Al-Si alloy (AA4147) but where the Al-Mn self-supporting surface was cooled more than about 5°C below the solidus temperature of the Al-Mn alloy, at which point the upper surface of the Al-Si alloy contacted the self-supporting surface of the Al-Mn alloy. The bond line 90 between the alloys is clearly visible indicating that a poor metallurgical bond was thereby formed. There is also an absence of exudates or dispersed intermetallic compositions of the first alloy in the second alloy.

[0098] A variety of alloy combinations were cast in accordance with the process of the present invention. The conditions were adjusted so that the first alloy surface temperature was between its solidus and liquidus temperature at the the upper surface of the second alloy. In all cases, the alloys were cast into ingots 690mm x 1590mm and 3 metres long and then processed by conventional preheating, hot rolling and cold rolling. The alloy combinations cast are given in Table 1 below. Using convention terminology, the "core" is the thicker supporting layer in a two alloy composite and the "cladding" is the surface functional layer. In the table, the First Alloy is the alloy cast first and the second alloy is the alloy brought into contact with the self-supporting surface of the first alloy.

TABLE 1

	First Alloy			Second Alloy
Cast	Location and alloy	L-S range (° C)	Casting temperature (°C)	Location and alloy	L-S range (° C)	Casting temperature (°C)
051804	Clad 0303	660-659	664-665	Core 3104	654-629	675-678
030826	Clad 1200	657-646	685-690	Core 2124	638-502	688-690
031013	Clad 0505	660-659	692-690	Core 6082	645-563	680-684
030827	Clad 1050	657-646	695-697	Core 6111	650-560	686-684

[0099] In each of these examples, the cladding was the first alloy to solidify and the core alloy was applied to the cladding alloy at a point where a self-supporting surface had formed, but where the surface temperature was still within the L-S range given above. This may be compared to the example above for brazing sheet where the cladding alloy had a lower melting range than the core alloy, in which case the cladding alloy (the "second alloy") was applied to the self supporting surface of the core alloy (the "first alloy"). Micrographs were taken of the interface between the cladding and the core in the above four casts. The micrographs were taken at 50X magnification. In each image the "cladding" layer appears to the left and the "core" layer to the right.

[0100] Figure 16 shows the interface of Cast #051804 between cladding alloy 0303 and core alloy 3104. The interface is clear from the change in grain structure in passing from the cladding material to the relatively more alloyed core layer

[0101] Figure 17 shows the interface of Cast #030826 between cladding alloy 1200 and core alloy 2124. The interface between the layers is shown by the dotted line 94 in the Figure. In this figure, the presence of alloy components of the 2124 alloy are present in the grain boundaries of the 1200 alloy within a short distance of the interface. These appear as spaced "fingers" of material in the Figure, one of which is illustrated by the numeral 95.' It can be seen that the 2124 alloy components extend for a distance of about 50 µm, which typically corresponds to a single grain of the 1200 alloy under these conditions.

[0102] Figure 18 shows the interface of Cast #031013 between cladding alloy 0505 and core alloy 6082 and Figure 19 shows the interface of Cast #030827 between cladding alloy 1050 and core alloy 6111. In each of these Figures the presence of alloy components of the core alloy are gain visible in the grain boundaries of the cladding alloy immediately adjacent the interface.

Claims

1. A method for the casting of a composite metal ingot comprising at least two layers formed of one or more alloys compositions, which comprises providing an open ended annular mould (10) having a feed end and an exit end wherein molten metal (18, 21) is added at the feed end and a solidified ingot is extracted from the exit end, and divider walls (14, 14a, 14') for dividing the feed end into at least two separate feed chambers, the divider walls terminating at bottom ends (35) thereof positioned above the exit end of said mould, with each feed chamber adjacent at least one other feed chamber, wherein for each pair of the adjacent feed chambers a first stream of a first alloy (18) is fed to one of the pair of feed chambers to form a pool of metal in the first chamber and a second stream of a second alloy (21) is fed through the second of the pair of feed chambers to form a pool of metal in the second chamber, the pools of metal each having an upper surface, contacting the first alloy pool with the divider wall between the pair chambers to thereby cool the first alloy pool to form a self-supporting surface (27) and allowing the second alloy pool to contact the first alloy pool such that the upper surface (34) of the second alloy pool contacts the divider wall at a position no more than 3 mm above the bottom end of the divider wall or contacts the self-supporting surface of the first alloy pool at a point where the temperature of the self-supporting surface is between the solidus and liquidus temperatures of the first alloy, whereby the two alloy pools are joined as two layers (20, 23), and cooling the joined alloy layers to form a composite ingot.

2. A method according to claim 1 wherein the first and second alloys have the same composition.

3. A method according to claim 1 wherein the first alloy and second alloys have different compositions.

4. A method according to claim 1 wherein the upper surface (34) of the second alloy contacts the self-supporting surface (27) of the first alloy at a position where the temperature of the self-supporting surface of the first alloy is between the solidus and liquidus temperatures thereof.

5. A method according to claim 4 wherein the upper surface (34) of the second alloy contacts the self-supporting surface (27) of the first alloy at a position where the temperature of the self-supporting surface of the first alloy is between the solidus and coherency temperatures thereof.

6. A method according to claim 1 wherein the temperature of the second alloy when it first contacts the self-supporting surface (27) of the first alloy is greater than or equal to the liquidus temperature of the second alloy.

7. A method according to any one of claims 1-6 wherein the divider walls (14, 14a, 14') for dividing the feed end consists of temperature controlled divider walls between each of the pair of chambers.

8. A method according to claim 7 wherein the temperature controlled divider walls (14, 14a, 14') serve to control the temperature of the self-supporting surface (27) of the first alloy (18) at the position where the upper surface (34) of the second alloy (21) contacts the self-supporting surface.

9. A method according to claim 7 wherein a temperature control fluid is contacted with the temperature controlled divider wall (14, 14a, 14') to control the heat removed or added via the divider wall.

10. A method according to claim 9 wherein the temperature control fluid flows through a closed channel (33) and the temperature of the self-supporting surface (27) is controlled by measuring the exit temperature of the fluid leaving the channel.

11. A method according to any one of claims 1-10 wherein the upper surface (34) of the second alloy pool is maintained at a level below the lower end of the divider wall (14, 14a, 14').

12. A method according to claim 11 where the upper surface (34) of the second alloy pool is maintained within 2 mm of the bottom edge of the divider wall (14, 14a, 14').

13. A method according to any one of claims 1-12 wherein the curvature of the divider wall 14, 14') is varied during casting.

14. A method according to any one of claims 1-12 wherein the divider wall (14, 14a, 14') is provided with an outward taper on the face in contact with the first alloy (18) .

15. A method according to claim 14 wherein the taper varies along the length of the divider wall (14, 14a, 14').

16. A method according to claim 1 wherein the position of one or more of the metal pool upper surfaces is controlled by providing a source of gas (51), delivering the gas by means of an open ended tube wherein the open end (53) is position at a reference point (54) within a chamber such that in use the open end will lie below the upper surface (55) in that chamber, controlling the flow rate of the gas to maintain a slow flow rate of gas through the tube at a rate sufficient to keep the tube open, measuring the pressure of the gas in the tube, comparing the measured pressure to a predetermined target and adjusting the flow of metal into the chamber to maintain the upper surface at a desired position.

17. A method according to claim 1 wherein the mould (10) has a rectangular cross-section and comprises two feed chambers of differing sizes oriented parallel to the long face (11) of the rectangular mould so as to form a rectangular ingot with cladding on one face.

18. A method according to claim 17 wherein the first alloy (18) is fed into the larger of the two feed chambers.

19. A method according to claim 17 wherein the second alloy (21) is fed into the larger of the two feed chambers.

20. A method according to claim 17, 18 or 19 wherein the divider wall (14, 14') is substantially parallel (44) to the long face (11) of the mould with curved end portions (45) that terminate (50) at the long walls of the mould.

21. A method according to claim 17, 18 or 19 wherein the divider wall (14, 14') is substantially parallel to the long face (11) of the mould with curved end portions that terminate at the short end walls of the mould.

22. A method according to claim 1 wherein the mould (10) has a rectangular cross-section and comprises three feed chambers oriented parallel to the long face (11) of the rectangular mould, wherein the central chamber is larger than either of the two side chambers so as to form a rectangular ingot with cladding (23) on two faces.

23. A method according to claim 22 wherein the first alloy (18) is fed to the central chamber.

24. A method according to claim 22 wherein the second alloy (21) is fed to the central chamber.

25. A method according to claim 22, 23 or 24 wherein the divider wall (14, 14') is substantially parallel (44) to the long face (11) of the mould with curved end portions (45) that terminate (50) at the long walls of the mould.

26. A method according to claim 22, 23 or 24 wherein the divider wall (14, 14') is substantially parallel to the long face (11) of the mould with curved end portions that terminate at the short end walls of the mould.

27. Casting apparatus for the production of composite metal ingots, comprising an open ended annular mould (10) having a feed end and an exit end and a moveable bottom block (17) adapted to fit within the exit end and movable in a direction along the axis of the annular mould, wherein the feed end of the mould is divided into at least two separate feed chambers, each feed chamber being adjacent at least one other feed chamber, and where adjacent pairs of feed chambers are separated by a temperature controlled divider wall (14, 14a, 14') terminating above the exit end of the mould, a means (15, 16) for delivering metal (18, 21) to each feed chamber, a means (31, 32) to control the flow of metal to each feed chamber, and a metal level control apparatus (51, 52, 53, 56) for each chamber such that in adjacent pairs of chambers the metal level in the first chamber can be maintained at a position above the lower end (35) of the said temperature controlled divider wall and in the second chamber can be maintained at a different position relative to the metal level in the first chamber.

28. A casting apparatus according to claim 27 wherein the metal level (34) in the second chamber can be maintained at a position below the lower end (35) of the divider wall.

29. A casting apparatus according to claim 27 wherein a closed channel (33) for temperature control fluid having an inlet (36) and an outlet (37) is connected with the temperature controlled divider wall (14, 14a, 14').

30. A casting apparatus according to claim 29 wherein a temperature measuring device (40) is provided at the fluid outlet (37).

31. A casting apparatus according to any one of claims 27-30 comprising a linear actuator (26) and control arm (25) attached to the temperature controlled divider wall (14) so that the curvature of the divider wall can be varied.

32. A casting apparatus according to any one of claims 27-30 wherein the temperature controlled divider wall (14) is tapered outwardly on the surface facing the first chamber.

33. A casting apparatus according to claim 32 wherein the taper is varied along the length of the divider wall.

34. A casting apparatus according to claim 27 comprising a graphite insert (46) on the surface of the temperature control divider wall (14) facing the first chamber.

35. A casting apparatus according to claim 27 comprising a fluid delivery channel (48) for providing a lubricant or separating layer to the surface of the divider wall.

36. A casting apparatus according to claim 34 wherein the graphite insert (46) is porous and one or more fluid delivery channels (48) in the temperature controlled divider wall (14) are adapted to deliver fluid via the porous graphite insert to the surface of the divider wall facing the first chamber.

37. A casting apparatus according to claim 27 wherein the metal level control apparatus comprises a source of gas 51), a flow controller (52) for controlling the flow of gas from the source, a tube connected to the flow controller at one end and open at the other end (53), and a pressure gauge (56) attached to the tube for measuring the pressure of gas in the tube, the open end of the tube being positioned within the chamber at a predetermined position (54) with respect to the body (10) of the mould, such that in use the open end of the tube is immersed in the metal in the chamber, wherein the means to control the flow of metal to the chamber is controlled in response to the measured pressure from the pressure gauge to maintain the metal level (55) at a predetermined position.

38. A casting apparatus according to claim 27 wherein the means to deliver metal to the chamber comprises a metal delivery trough (59) and one or more open ended metal delivery tubes (58) connected to the trough.

39. A casting apparatus according to claim 38 wherein the one or more open ended tubes is positioned within the chamber so that in use the open end is immersed in metal.

Ansprüche

1. Verfahren zum Gießen eines Verbundmetall-Gussblocks, umfassend zumindest zwei Schichten, die aus einer oder mehreren Legierungszusammensetzungen ausgebildet sind, welches das Bereitstellen einer ringförmigen Gussform (10) mit offenem Ende mit einem Zufuhrende und einem Austrittsende umfasst, wobei geschmolzenes Metall (18, 21) am Zufuhrende zugeben wird und ein erstarrter Gussblock aus dem Austrittsende herausgezogen wird, sowie Teilerwände (14, 14a, 14') zur Unterteilung des Zufuhrendes in zumindest zwei unterschiedliche Zufuhrkammern, wobei die Teilerwände an deren Bodenenden (35), die oberhalb des Austrittsendes der Gussform positioniert sind, enden, wobei jede Zufuhrkammer zumindest zu einer anderen Zufuhrkammer benachbart ist und wobei für jedes Paar benachbarter Zufuhrkammern ein erster Strom einer ersten Legierung (18) zu einem von dem Paar von Zufuhrkammern zugeführt wird, um einen Pool aus Metall in der ersten Kammer auszubilden, und ein zweiter Strom einer zweiten Legierung (21) durch die zweite des Paars von Zufuhrkammern zugeführt wird, um einen Pool aus Metall in der zweiten Kammer auszubilden, die Pools aus Metall jeweils eine obere Oberfläche aufweisen, die den ersten Legierungspool mit der Teilerwand zwischen dem Paar von Kammern berührt, um hierdurch den ersten Legierungspool abzukühlen, um eine sich selbst tragende Oberfläche (27) auszubilden und es dem zweiten Legierungspool zu ermöglichen, den ersten Legierungspool derart zu berühren, dass die obere Oberfläche (34) des zweiten Legierungspools die Teilerwand an einer Position nicht mehr als 3 mm oberhalb des Bodenendes der Teilerwand berührt oder die selbsttragende Oberfläche des ersten Legierungspools an einem Punkt berührt, wo die Temperatur der selbsttragenden Oberfläche zwischen den Solidus- und Liquidus-Temperaturen der ersten Legierung liegt, wodurch die zwei Legierungspools als zwei Schichten (20, 23) miteinander verbunden werden, und Abkühlen der verbundenen Legierungsschichten, um einen Verbund-Gussblock auszubilden.

2. Verfahren gemäß Anspruch 1, wobei die ersten und zweiten Legierungen die gleiche Zusammensetzung aufweisen.

3. Verfahren gemäß Anspruch 1, wobei die erste Legierung und die zweite Legierung unterschiedliche Zusammensetzungen aufweisen.

4. Verfahren gemäß Anspruch 1, wobei die obere Oberfläche (34) der zweiten Legierung die selbsttragende Oberfläche (27) der ersten Legierung an einer Position berührt, wo die Temperatur der selbsttragenden Oberfläche der ersten Legierung zwischen deren Solidus- und Liquidus-Temperatur liegt.

5. Verfahren gemäß Anspruch 4, wobei die obere Oberfläche (34) der zweiten Legierung die selbsttragende Oberfläche (27) der ersten Legierung an einer Position berührt, wo die Temperatur der selbsttragenden Oberfläche der ersten Legierung zwischen der Solidus- und der Kohärenz-Temperatur hiervon liegt.

6. Verfahren gemäß Anspruch 1, wobei die Temperatur der zweiten Legierung dann, wenn sie zuerst die selbsttragende Oberfläche (27), der ersten Legierung berührt, größer als oder gleich der Liquidus-Temperatur der zweiten Legierung ist.

7. Verfahren gemäß einen der Ansprüche 1 bis 6, wobei die Teilerwände (14, 14a, 14') zur Unterteilung des Zufuhrendes aus temperaturgeregelten Teilerwänden zwischen jedem der Paare von Kammern bestehen.

8. Verfahren gemäß Anspruch 7, wobei die temperaturgeregelten Teilerwände (14, 14a, 14') dazu dienen, die Temperatur der selbsttragenden Oberfläche (27) der ersten Legierung (18) an einer Position zu regeln, wo die obere Oberfläche (34) der zweiten Legierung (21) die selbsttragende Oberfläche berührt.

9. Verfahren gemäß Anspruch 7, wobei ein Temperaturregelungsfluid mit der temperaturgeregelten Teilerwand (14, 14a, 14') in Kontakt tritt, um die über die Teilerwand abgeführte oder zugegebene Wärme zu regeln.

10. Verfahren gemäß Anspruch 9, wobei das Temperaturregelungsfluid durch einen geschlossenen Kanal (33) hindurchströmt und die Temperatur der selbsttragenden Oberfläche (27) durch Messen der Austrittstemperatur des den Kanal verlassenden Fluids geregelt wird.

11. Verfahren gemäß einem der Ansprüche 1 bis 10, wobei die obere Oberfläche (34) des zweiten Legierungspools an einem Niveau unterhalb des unteren Endes der Teilerwand (14, 14a, 14') beibehalten wird.

12. Verfahren gemäß Anspruch 11, wobei die obere Oberfläche (34) des zweiten Legierungspools innerhalb von 2 mm von der Bodenkante der Teilerwand (14, 14a, 14') beibehalten wird.

13. Verfahren gemäß einem der Ansprüche 1 bis 12, wobei die Krümmung der Teilerwand (14, 14') während des Gießens variiert wird.

14. Verfahren gemäß einem der Ansprüche 1 bis 12, wobei die Teilerwand (14, 14a, 14') mit einer nach außen gerichteten Abschrägung an der Fläche versehen ist, die in Kontakt mit der ersten Legierung (18) steht.

15. Verfahren gemäß Anspruch 14, wobei die Abschrägung entlang der Länge der Teilerwand (14, 14a, 14') variiert.

16. Verfahren gemäß Anspruch 1, wobei die Position einer oder mehrerer der oberen Oberflächen des Metallpools durch Bereitstellen einer Gasquelle (51) geregelt wird, die das Gas mittels eines Rohrs mit offenem Ende zuführt, wobei das offene Ende (53) die Position an einem Bezugspunkt (54) innerhalb einer Kammer ist, so dass das offene Ende im Gebrauch unterhalb der oberen Oberfläche (55) in dieser Kammer liegt, die Strömungsrate des Gases geregelt wird, um eine langsame Strömungsrate des Gases durch das Rohr beizubehalten, die ausreicht, das Rohr offen zu halten, des Messens des Drucks des Gases in dem Rohr, der gemessene Druck mit einem vorab festgelegten Zieldruck verglichen wird und die Strömung des Metalls in die Kammer hinein eingestellt wird, um die obere Oberfläche bei einer gewünschten Position beizubehalten.

17. Verfahren gemäß Anspruch 1, wobei die Gussform (10) einen rechteckigen Querschnitt aufweist und zwei Zufuhrkammern unterschiedlicher Größe umfasst, die parallel zur langen Fläche (11) der rechteckigen Gussform ausgerichtet sind, um einen rechteckigen Gussblock mit einer Plattierung auf einer Fläche auszubilden.

18. Verfahren gemäß Anspruch 17, wobei die erste Legierung (18) in die größere der zweiten Zufuhrkammern zugeführt wird.

19. Verfahren gemäß Anspruch 17, wobei die zweite Legierung (21) in die größere der zwei Zufuhrkammern zugeführt wird.

20. Verfahren gemäß Anspruch 17, 18 oder 19, wobei die Teilerwand (14, 14') im Wesentlichen parallel (44) zur langen Fläche (11) der Gussform mit gekrümmten Endabschnitten (45), die an den langen Wänden der Gussform enden (50), steht.

21. Verfahren gemäß Anspruch 17, 18 oder 19, wobei die Teilerwand (14, 14') im Wesentlichen parallel zur langen Fläche (11) der Gussform mit gekrümmten Endabschnitten, die an den kurzen Endwänden der Gussform enden, steht.

22. Verfahren gemäß Anspruch 1, wobei die Gussform (10) einen rechteckigen Querschnitt aufweist und drei Zufuhrkammern umfasst, die parallel zur langen Fläche (11) der rechteckigen Gussform ausgerichtet sind, wobei die zentrale Kammer größer als beide Seitenkammern ist, um so einen rechteckigen Gussblock mit Plattierungen (23) an zwei Flächen auszubilden.

23. Verfahren gemäß Anspruch 22, wobei die erste Legierung (18) zur zentralen Kammer zugeführt wird.

24. Verfahren gemäß Anspruch 22, wobei die zweite Legierung (21) zur zentralen Kammer zugeführt wird.

25. Verfahren gemäß Anspruch 22, 23 oder 24, wobei die Teilerwand (14, 14') im Wesentlichen parallel (44) zur langen Fläche (11) der Gussform mit gekrümmten Endabschnitten (45), die an den langen Wänden der Gussform enden (50), steht.

26. Verfahren gemäß Anspruch 22, 23 oder 24, wobei die Teilerwand (14, 14') im Wesentlichen parallel zur langen Fläche (11) der Gussform mit gekrümmten Endabschnitten, die an den kurzen Endwänden der Gussform enden, steht.

27. Gießvorrichtung für die Herstellung von Verbundmetall-Gussblöcken, umfassend eine ringförmige Gussform (10) mit offenem Ende, welche ein Zufuhrende sowie ein Austrittsende sowie einen beweglichen Bodenblock (17) aufweist, der so angepasst ist, dass er in das Austrittsende einpasst und in einer Richtung entlang der Achse der ringförmigen Gussform beweglich ist, wobei das Zufuhrende der Gussform in zumindest zwei unterschiedliche Zufuhrkammern unterteilt ist, jede Zufuhrkammer zumindest zu einer anderen Zufuhrkammer benachbart ist, und wobei benachbarte Paare von Zufuhrkammern durch eine temperaturgeregelte Teilerwand (14, 14a, 14') unterteilt ist, die oberhalb des Austrittsendes der Gussform enden, ein Mittel (15, 16) zur Zufuhr von Metall (18, 21) zu jeder Zufuhr, ein Mittel (31, 32) zur Steuerung des Stroms von Metall zu jeder Zufuhrkammer, sowie eine Regelungsvorrichtung für das Metallniveau (51, 52, 53, 56) für jede Kammer, so dass das Metallniveau in benachbarten Paaren von Kammern in der ersten Kammer bei einer Position oberhalb des unteren Endes (35) der temperaturgeregelten Teilerwand beibehalten werden kann und in der zweiten Kammer bei einer anderen Position in Bezug auf das Metallniveau in der ersten Kammer beibehalten werden kann.

28. Gießvorrichtung gemäß Anspruch 27, wobei das Metallniveau (34) in der zweiten Kammer bei einer Position unterhalb des unteren Endes (35) der Teilerwand beibehalten werden kann.

29. Gießvorrichtung gemäß Anspruch 27, wobei ein geschlossener Kanal (33) für ein Temperaturregelungsfluid mit einem Einlass (36) und einem Auslass (37) mit der temperaturgeregelten Teilerwand (14, 14a, 14') verbunden ist.

30. Gießvorrichtung gemäß Anspruch 29, wobei eine Temperaturmessvorrichtung (40) am Fluidauslass (37) vorgesehen ist.

31. Gießvorrichtung gemäß einem der Ansprüche 27 bis 30, umfassend einen linearen Betätiger (26) und einen Regelungsarm (25), der an der temperaturgeregelten Teilerwand (14) so angebracht ist, dass die Krümmung der Teilerwand variiert werden kann.

32. Gießvorrichtung gemäß einem der Ansprüche 27 bis 30, wobei die temperaturgeregelte Teilerwand (14) nach außen an der Oberfläche, die der ersten Kammer gegenübersteht, abgeschrägt ist.

33. Gießvorrichtung gemäß Anspruch 32, wobei die Abschrägung entlang der Länge der Teilerwand variiert ist.

34. Gießvorrichtung gemäß Anspruch 27, umfassend einen Graphiteinsatz (46) an der Oberfläche der temperaturgeregelten Teilerwand (14), die der ersten Kammer gegenübersteht.

35. Gießvorrichtung gemäß Anspruch 27, umfassend einen Fluidzufuhrkanal (48) zur Bereitstellung eines Schmiermittels oder einer Trennschicht auf der Oberfläche der Teilerwand.

36. Gießvorrichtung gemäß Anspruch 34, wobei der Graphiteinsatz (46) porös ist und ein oder mehrere Fluid-Zufuhrkanäle (48) in der temperaturgeregelten Teilerwand (14) so angepasst sind, dass sie ein Fluid über den porösen Graphiteinsatz zur Oberfläche der Teilerwand, die der ersten Kammer gegenübersteht, zuführen.

37. Gießvorrichtung gemäß Anspruch 27, wobei die Regelungsvorrichtung für das Metallniveau eine Gasquelle (51), einen Strömungsregler (52) zur Regelung des Gasstroms von der Quelle, ein mit dem Strömungsregler an einem Ende verbundenes und zum anderen Ende (53) offenes Rohr, sowie eine Druckanzeige in dem Rohr umfasst, wobei das offene Ende des Rohrs innerhalb der Kammer an einer vorab festgelegten Position (54) in Bezug auf den Körper (10) der Gussform derart positioniert ist, dass das offene Ende des Rohrs bei der Verwendung in das Metall in der Kammer eingetaucht ist, wodurch das Mittel zur Regelung des Metallstroms zur Kammer als Reaktion auf den gemessenen Druck von der Druckanzeige geregelt wird, um das Metallniveau (55) bei einer vorab festgelegten Position beizubehalten.

38. Gießvorrichtung gemäß Anspruch 27, wobei das Mittel zur Zufuhr von Metall zur Kammer eine Metallzufuhrrinne (59) an einer oder mehreren Zufuhrrohren (58) mit offenem Ende, die mit der Rinne verbunden sind, umfasst.

39. Gießvorrichtung gemäß Anspruch 38, wobei das eine oder die mehreren Rohre mit offenem Ende innerhalb der Kammer so positioniert sind, dass das offene Ende im Gebrauch in das Metall eingetaucht ist.

Revendications

1. Procédé de coulage d'un lingot de métal composite comprenant au moins deux couches formées d'une ou plusieurs compositions d'alliages, qui comprend la fourniture d'un moule annulaire (10) aux extrémités ouvertes, ayant une extrémité d'alimentation et une extrémité de sortie, dans lequel on ajoute du métal fondu (18, 21) à l'extrémité d'alimentation et on extrait un lingot solidifié de l'extrémité de sortie, et des parois séparatrices (14, 14a, 14') pour diviser l'extrémité d'alimentation en au moins deux chambres d'alimentation séparées, les parois séparatrices se terminant à leurs extrémités inférieures (35) positionnées au-dessus de l'extrémité de sortie dudit moule, chaque chambre d'alimentation étant adjacente à au moins une autre chambre d'alimentation, dans lequel, pour chaque paire des chambres d'alimentation adjacentes, un premier courant d'un premier alliage (18) est acheminé à une première paire des chambres d'alimentation en vue de former un bain de métal dans la première chambre et un second courant d'un second alliage (21) est acheminé à travers la seconde paire des chambres d'alimentation en vue de former un bain de métal dans la seconde chambre, les bains de métal ayant chacun une surface supérieure, la mise en contact du premier bain d'alliage avec la paroi séparatrice entre les deux chambres pour refroidir de la sorte le premier bain d'alliage afin de former une surface autoportante (27), et le fait de laisser le second bain d'alliage venir en contact avec le premier bain d'alliage de sorte que la surface supérieure (34) du second bain d'alliage vienne en contact avec la paroi séparatrice dans une position ne dépassant pas plus de 3 mm au-dessus de l'extrémité inférieure de la paroi séparatrice ou vienne en contact avec la surface autoportante du premier bain d'alliage en un point où la température de la surface autoportante se situe entre les températures de solidus et de liquidus du premier alliage, de sorte que les deux bains d'alliage soient joints en deux couches (20,23), et le refroidissement des couches d'alliage jointes pour former un lingot composite.

2. Procédé selon la revendication 1, dans lequel le premier et le second alliage ont la même composition.

3. Procédé selon la revendication 1, dans lequel le premier et le second alliage ont des compositions différentes.

4. Procédé selon la revendication 1, dans lequel la surface supérieure (34) du second alliage est en contact avec la surface autoportante (27) du premier alliage dans une position où la température de la surface autoportante du premier alliage se situe entre ses températures de solidus et de liquidus.

5. Procédé selon la revendication 4, dans lequel la surface supérieure (34) du second alliage est en contact avec la surface autoportante (27) du premier alliage dans une position où la température de la surface autoportante du premier alliage se situe entre ses températures de solidus et de cohérence.

6. Procédé selon la revendication 1, dans lequel la température du second alliage lorsqu'il est la première fois en contact avec la surface autoportante (27) du premier alliage est supérieure ou égale à la température de liquidus du second alliage.

7. Procédé selon l'une quelconque des revendications 1 à 6, dans lequel les parois séparatrices (14, 14a, 14') pour diviser l'extrémité d'alimentation sont constituées de parois séparatrices commandées en température, entre chacune des deux chambres.

8. Procédé selon la revendication 7, dans lequel les parois séparatrices commandées en température (14, 14a, 14') servent à commander la température de la surface autoportante (27) du premier alliage (18) dans la position où la surface supérieure (34) du second alliage (21) vient en contact avec la surface autoportante.

9. Procédé selon la revendication 7, dans lequel on met en contact un fluide de commande de température avec la paroi séparatrice commandée en température (14, 14a, 14') pour commander la chaleur éliminée ou ajoutée via la paroi séparatrice.

10. Procédé selon la revendication 9, dans lequel le fluide de commande de la température s'écoule à travers un canal fermé (33) et la température de la surface autoportante (27) est commandée par mesure de la température de sortie du fluide quittant le canal.

11. Procédé selon l'une quelconque des revendications 1 à 10, dans lequel on maintient la surface supérieure (34) du second bain d'alliage à un niveau situé au-dessous de l'extrémité inférieure de la paroi séparatrice (14, 14a, 14').

12. Procédé selon la revendication 11, dans lequel on maintient la surface supérieure (34) du second bain d'alliage dans les 2 mm du bord inférieur de la paroi séparatrice (14, 14a, 14').

13. Procédé selon l'une quelconque des revendications 1 à 12, dans lequel la courbure de la paroi séparatrice (14, 14') est modifiée au cours du coulage.

14. Procédé selon l'une quelconque des revendications 1 à 12, dans lequel la paroi séparatrice (14, 14a, 14') présente une conicité vers l'extérieur sur la face en contact avec le premier alliage (18).

15. Procédé selon la revendication 14, dans lequel la conicité varie sur la longueur de la paroi séparatrice (14, 14a, 14').

16. Procédé selon la revendication 1, dans lequel on commande la position d'une ou plusieurs surfaces supérieures de bain de métal par la mise en oeuvre d'une source gazeuse (51), la délivrance du gaz au moyen d'un tube à extrémité ouverte, dans lequel l'extrémité ouverte (53) est positionnée en un point de référence (54) à l'intérieur de la chambre de sorte que, en service, l'extrémité ouverte se trouve au-dessous de la surface supérieure (55) dans cette chambre, la commande du débit du gaz pour maintenir un débit de gaz lent à travers le tube suffisamment pour maintenir le tube ouvert, la mesure de la pression du gaz dans le tube, la comparaison de la pression mesurée à une cible prédéterminée, et l'ajustement de l'écoulement de métal dans la chambre afin de maintenir la surface supérieure dans une position souhaitée.

17. Procédé selon la revendication 1, dans lequel le moule (10) a une coupe transversale rectangulaire et comprend deux chambres d'alimentation de dimensions différentes orientées parallèlement à la longue face (11) du moule rectangulaire afin de former un lingot rectangulaire avec un gainage sur une face.

18. Procédé selon la revendication 17, dans lequel le premier alliage (18) est acheminé dans la plus grande des deux chambres d'alimentation.

19. Procédé selon la revendication 17, dans lequel le second alliage (21) est acheminé dans la plus grande des deux chambres d'alimentation.

20. Procédé selon la revendication 17, 18 ou 19, dans lequel la paroi séparatrice (14, 14') est sensiblement parallèle (44) à la longue face (11) du moule avec des parties d'extrémité incurvées (45) qui se terminent (50) sur les longues parois du moule.

21. Procédé selon la revendication 17, 18 ou 19, dans lequel la paroi séparatrice (14, 14') est sensiblement parallèle à la longue face (11) du moule avec des parties d'extrémité incurvées qui se terminent sur les courtes parois d'extrémité du moule.

22. Procédé selon la revendication 1, dans lequel le moule (10) a une coupe transversale rectangulaire et comprend trois chambres d'alimentation orientées parallèlement à la longue face (11) du moule rectangulaire, dans lequel la chambre centrale est plus grande que l'une et l'autre des deux chambres latérales afin de former un lingot rectangulaire avec un gainage (23) sur les deux faces.

23. Procédé selon la revendication 22, dans lequel le premier alliage (18) est acheminé à la chambre centrale.

24. Procédé selon la revendication 22, dans lequel le second alliage (21) est acheminé à la chambre centrale.

25. Procédé selon la revendication 22, 23 ou 24, dans lequel la paroi séparatrice (14, 14') est sensiblement parallèle (44) à la longue face (11) du moule avec des parties d'extrémité incurvées (45) qui se terminent (50) sur les longues parois du moule.

26. Procédé selon la revendication 22, 23 ou 24, dans lequel la paroi séparatrice (14, 14') est sensiblement parallèle à la longue face (11) du moule avec des parties d'extrémité incurvées qui se terminent sur les courtes parois d'extrémité du moule.

27. Appareil de coulage destiné à la production de lingots de métaux composites, comprenant un moule annulaire (10) aux extrémités ouvertes ayant une extrémité d'alimentation et une extrémité de sortie et un bloc inférieur mobile (17) à même de s'ajuster dans l'extrémité de sortie et déplaçable dans une direction le long de l'axe du moule annulaire, dans lequel l'extrémité d'alimentation du moule est divisé en au moins deux chambres d'alimentation séparées, chaque chambre d'alimentation étant adjacente à au moins une autre chambre d'alimentation, et où des paires adjacentes de chambres d'alimentation sont séparées par une paroi séparatrice commandée en température (14, 14a, 14') se terminant au-dessus de l'extrémité de sortie du moule, un moyen (15, 16) servant à acheminer du métal (18, 21) à chaque chambre d'alimentation, un moyen (31, 32) pour commander l'écoulement de métal à chaque chambre d'alimentation, et un appareil de commande de niveau de métal (51, 52, 53, 56) pour chaque chambre de sorte que, dans des paires adjacentes de chambres, on puisse maintenir le niveau de métal, dans la première chambre, dans une position au-dessous de l'extrémité inférieure (35) de ladite paroi séparatrice commandée en température et, dans la seconde chambre, dans une position différente par rapport au niveau de métal dans la première chambre.

28. Appareil de coulage selon la revendication 27, dans lequel on peut maintenir le niveau de métal (34) dans la seconde chambre dans une position au-dessous de l'extrémité inférieure (35) de la paroi séparatrice.

29. Appareil de coulage selon la revendication 27, dans lequel un canal fermé (33) pour un fluide de commande de température, ayant une entrée (36) et une sortie (37), est raccordé à la paroi séparatrice commandée en température (14, 14a, 14').

30. Appareil de coulage selon la revendication 29, dans lequel un dispositif de mesure de température (40) est prévu à la sortie de fluide (37).

31. Appareil de coulage selon l'une quelconque des revendications 27 à 30, comprenant un dispositif d'actionnement linéaire (26) et un bras de commande (25) fixé à la paroi séparatrice commandée en température (14) de sorte que la courbure de la paroi séparatrice puisse être modifiée.

32. Appareil de coulage selon l'une quelconque des revendications 27 à 30, dans lequel la paroi séparatrice commandée en température (14) est conformée en cône vers l'extérieur sur la surface en regard de la première chambre.

33. Appareil de coulage selon la revendication 32, dans lequel on fait varier la conicité sur la longueur de la paroi séparatrice.

34. Appareil de coulage selon la revendication 27, comprenant une pièce rapportée de graphite (46) sur la surface de la paroi séparatrice commandée en température (14) en regard de la première chambre.

35. Appareil de coulage selon la revendication 27, comprenant un canal d'acheminement de fluide (48) pour fournir une couche lubrifiante ou séparatrice à la surface de la paroi séparatrice.

36. Appareil de coulage selon la revendication 34, dans lequel la pièce rapportée de graphite (46) est poreuse et un ou plusieurs canaux d'acheminement de fluide (48) dans la paroi séparatrice commandée en température (14) sont adaptés pour acheminer du fluide via la pièce rapportée en graphite poreux à la surface de la paroi séparatrice en regard de la première chambre.

37. Appareil de coulage selon la revendication 27, dans lequel l'appareil de commande de niveau de métal comprend une source gazeuse (51), un dispositif de commande d'écoulement (52) pour commander l'écoulement de gaz depuis la source, un tube raccordé au dispositif de commande d'écoulement à une extrémité et ouvert à l'autre extrémité (53), et une jauge de pression (56) fixée au tube pour mesurer la pression du gaz dans le tube, l'extrémité ouverte du tube étant positionnée à l'intérieur de la chambre dans une position prédéterminée (54) par rapport au corps (10) du moule, de sorte que, en service, l'extrémité ouverte du tube soit immergée dans le métal dans la chambre, dans lequel le moyen de commande de l'écoulement de métal à la chambre est commandé en réponse à la pression mesurée depuis la jauge de pression pour maintenir le niveau de métal (55) dans une position prédéterminée.

38. Appareil de coulage selon la revendication 27, dans lequel le moyen permettant d'acheminer du métal à la chambre comprend une gouttière d'acheminement de métal (59) et un ou plusieurs tubes d'acheminement de métal (58) à extrémités ouvertes, raccordés à la gouttière.

39. Appareil de coulage selon la revendication 38, dans lequel le ou les tubes à extrémités ouvertes sont positionnés à l'intérieur de la chambre, de sorte qu'en service, l'extrémité ouverte soit immergée dans le métal.

Drawing